The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 101 18 508.1, filed on Apr. 12, 2001, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing a fibrous material web, in particular paper or cardboard web.
2. Discussion of Background Information
In the previously known apparatuses for paper manufacture, retention is determined on-line through the stock consistencies measured in the back water and in the stock feed to the headbox, and is kept constant through regulation of the retention agent quantity or quantities. A known paper apparatus with retention regulation of this nature is shown schematically in FIG. 1.
This method based on a regulation of retention has, among other things, the disadvantage that formation becomes increasingly worse as retention becomes greater. To avoid poor formation, the retention must be set for the maximum possible retention with a large safety margin.
In this connection, formation is generally understood to mean the structure and degree of uniformity of fiber distribution in the fibrous material web, e.g. paper, either measured or evaluated, e.g. by light sent through. Formation is generally also referred to as the xe2x80x9clook-throughxe2x80x9d of the fibrous material web or of the paper. Retention is understood to mean the proportion of the mass retained by the wire or wires relative to the total mass applied to the wire.
The present invention provides an improved method and an improved apparatus of the aforementioned type, in which the aforementioned disadvantages are eliminated.
In this regard, the invention provides a method for manufacturing a fibrous material web, in particular paper or cardboard web, in which the formation of the fibrous material web is measured on-line as a controlled variable and is maintained at a preselectable target level via an automatic formation regulator.
In this connection, the formation can be maintained at the preselectable target level in particular by appropriately changing the added quantity of at least one retention agent.
According to one preferred practical embodiment of the method in accordance with the invention, the retention is continually maintained at the respective maximum possible value.
In that two different retention agents are advantageously added at two different points (dual system), the retention can also be constantly maintained at a preselectable high level. Advantageously, the formation is maintained at the preselectable target level through appropriately changing the ratio of the added quantities of the two retention agents.
In this connection, formation regulation can be performed in various ways. A few possibilities are mentioned below purely by way of example.
Thus, for instance, formation can be set or regulated in that two retention agent mass flows QR1, QR2 at a constant ratio QR1/QR2 are changed appropriately, or increased or reduced.
Another possibility includes, for example, that the formation is measured, the measured value is compared to a target value, the added quantity of a first retention agent of a dual system is adjusted appropriately to match the formation to the target value, and in order to set the highest possible level of retention the added quantity of a second retention agent of the dual system, or the ratio between the added quantities of the two retention agents, is corrected up to the point where the formation begins to worsen again.
Moreover, it is possible, for example, to superimpose the formation regulation on a retention regulation. In this connection the retention regulation, which can be accomplished in a conventional manner, can in particular be faster than the formation regulation.
The two different retention agents can, for example, include polymers with different charge densities (anionic/cationic) and/or different molecular weights. In this connection, the two different retention agents can include, e.g., polyethylene imine (PEI) and polyacrylamide (PAM).
In accordance with another practical embodiment of the method in accordance with the invention, the first retention agent includes a polymer, e.g. polyacrylamide, and the second retention agent includes inorganic microparticles, e.g. bentonite, hydrocol, etc. Thus, for example, one polymer can be provided for coarse flocculation and one agent for fine flocculation.
In certain cases, it is advantageous if raw material influences and/or the water flow in the wet section are also included in formation regulation. This is possible through the use of fuzzy logic and/or predictive controls, in particular.
Thus, for example, when short-fibered raw materials are used, the formation is worsened to a lesser extent with increasing retention than when long-fibered materials are employed.
This material-dependent relationship between formation and retention can be taken into account in the control algorithm. This can be accomplished, for example, within the framework of a formation regulation superimposed over a retention regulation, or in that the ratio QR1/QR2 of the mass flows of the retention agents of the dual system are also selected by fiber type (raw material type).
The apparatus in accordance with the invention for manufacturing a fibrous material web, in particular paper or cardboard web, accordingly includes an automatic formation regulator in which the formation of the fibrous material web is measured on-line as a controlled variable and is maintained at a preselectable target level.
The present invention is directed to a process for manufacturing a fibrous material web in an apparatus having an automatic formation regulator. The process includes on-line measuring of formation of the fibrous material web, utilizing the on-line measured formation as a controlled variable, and maintaining the formation at a preselectable target level via the automatic formation regulator.
According to a feature of the instant invention, the fibrous material web can include one of a paper or cardboard web.
In accordance with another feature of the invention, the formation can be maintained at the preselectable target level by changing an added quantity of at least one retention agent.
The process can further include continually maintaining retention at a maximum possible value.
Further, different retention agents may be added at different points, and the process can further include adjusting the retention. The two different retention agents may include polyethylene imine (PEI) and polyacrylamide (PAM).
Moreover, two different retention agents can be added at two different points, and the process may further include constantly maintaining the retention at a preselectable high level.
According to still another feature of the invention, two different retention agents may be added at two different points, and the process can further include maintaining the formation at the preselectable target level by changing a ratio of added quantities of the two different retention agents.
In accordance with another feature of the present invention, two different retention agents can be added at two different points, and the two different retention agents may include polymers with at least one of different charge densities and different molecular weights. The different charge densities may include anionic/cationic differences.
The process can further include one of adjusting or regulating the formation by one of increasing and decreasing a constant ratio QR1/QR2, wherein QR1 and QR2 represent retention agent mass flows.
After the on-line measurement of the formation, the process may further include comparing the measured value to a target value, adjusting an added quantity of a first retention agent of a dual system to match the formation to the target value, and correcting one of an added quantity of a second retention agent and a ratio between the added quantities of the two retention agents to a point at which the formation begins to worsen. Further, the correcting enables the setting of a highest possible level of retention.
In accordance with a further feature of the present invention, the formation regulation may be superimposed on a retention regulation.
Two different retention agents can be added at two different points, such that a first retention agent may include a polymer and a second retention agent may include inorganic microparticles. Further, the polymer can include polyacrylamide and the inorganic microparticles can include at least one of bentonite and hydrocol.
According to the invention, at least one of raw material influences and water flow in a wet section can be included in formation regulation.
Further, in accordance with the invention, formation regulation may utilize at least one of fuzzy logic and predictive controls.
In accordance with still another feature of the instant invention, at least one of at least one on-line measured formation value and at least one stock consistency value can be input into a controller for regulating the formation, and the process may further include adjusting a level of the formation by using a manipulated variable output by the controller to adjust one of a mass flow rate or volume flow rate of at least one retention agent. Moreover, the at least one stock consistency value can include at least one of the stock consistency value of the low consistency back water and the stock consistency value of the high consistency fiber suspension to the headbox. The low consistency back water may include white water. Further, at least one value for at least one stock parameter may be input to the controller as an additional input variable.
The present invention is directed to an apparatus for manufacturing a fibrous material web that includes an on-line measuring device structured and arranged to measure formation of the fibrous material web, and an automatic formation regulator structured and arranged to receive the formation of the fibrous material web from the on-line measuring device as a controlled variable, and to maintained the formation at a preselectable target level.
According to a feature of the invention, the apparatus can further include a device for changing an added quantity of at least one retention agent. The changing of the added quantity of the at least one retention agent can maintain the formation at the preselectable target level.
That apparatus can further include a device to continually maintain retention at a respective maximum possible value.
Moreover, the apparatus may include devices for adding two different retention agents at two different points, and a device structured and arranged to constantly maintain the retention at a preselectable high level.
In accordance with a further feature of the invention, the apparatus may further include devices for adding two different retention agents at two different points, and a device structured and arranged to maintain the formation at the preselectable target level by changing quantities of the two added retention agents.
The apparatus can also include devices for adding two different retention agents at two different points. The two different retention agents may include polymers with at least one of different charge densities and different molecular weights. Further, the different charge densities can include anionic/cationic differences.
In accordance with another feature of the present invention, the apparatus may further include a device for one of adjusting or regulating the formation by one of increasing and decreasing a constant ratio QR1/QR2, wherein QR1 and QR2 represent retention agent mass flows.
Further, the apparatus may include a device for comparing a measured formation value to a target value, a device for adjusting an added quantity of a first retention agent of a dual system to match the formation to the target value, and a device for correcting one of an added quantity of a second retention agent and a ratio between the added quantities of the two retention agents to a point at which the formation begins to worsen. The device for correcting may enable the setting of a highest possible level of retention.
According to the invention, the automatic formation regulator may be superimposed on a retention regulator.
In accordance with still another feature of the instant invention, the apparatus may include a device for adding different retention agents at different points, and a device for adjusting retention. The two different retention agents may include polyethylene imine (PEI) and polyacrylamide (PAM).
According to a still further feature, the apparatus can include a device for adding two different retention agents at two different points. A first retention agent may include a polymer and a second retention agent may include inorganic microparticles. The polymer can include polyacrylamide and the inorganic microparticles can include at least one of bentonite and hydrocol.
Moreover, the automatic formation regulator may be coupled receive data related to at least one of raw material influences and water flow in a wet section.
Still further, the automatic formation regulator can utilize at least one of fuzzy logic and predictive controls.
In accordance with yet another feature of the present invention, the automatic formation regulator can be structured and arranged to receive as input at least one of at least one on-line measured formation value and at least one stock consistency value, and the automatic formation regulator may be structured and arranged to adjust a level of the formation by using a manipulated variable output in order to adjust one of a mass flow rate or volume flow rate of at least one retention agent. The at least one stock consistency value can include at least one of the stock consistency value of the low consistency back water and the stock consistency value of the high consistency fiber suspension to the headbox. The low consistency back water may include white water. Further, at least one value for at least one stock parameter may be input to the automatic formation regulator as an additional input variable.